[R-390] 4kc filter position silent

[Frank Hughes]

Hi,

Trying to locate the trouble w/ my R-390A 4kc filter.

Works fine in all other filter selections, but 4kc is now silent.

Looking at the schematic, seems like either the filter might be open or
possibly

a trimmer is dirty?

Also noted C509, C514 need to be checked.

I had retired this particular R-390A a few years ago, after finding a
pristine R-390/URR to use for AM nets.

(My ears like the R-390/URR audio a little better, don’t know why)

But now I need to use this R-390A for SSB (CV-591A attached), having a 4kc
filter would be handy.

Other than just swapping in another 4kc filter to isolate the issue, and
checking the capacitors associated with this filter, is there anything else
I should be looking for while I have it apart?

I have a hoard of mechanical filters of various KC values around here
somewhere, but as the foam inside them seems to decay with each passing
day, might have a pile of junk spare filters by now.

73

Frank

KJ4OLL


PS: I even knew how to test these, out of circuit, at one time.

Why can I remember what a 1950’s TV commercial “LSMFT” stands for, but
can’t recall exactly what the setup was I used to test these stoopit
mechanical filters????

https://www.youtube.com/watch?v=3R3ja4WYjCc&t=17s